1. Field of the Invention
The present invention is generally related to nuclear reactor installations and more particularly to a reactor vessel cavity seal plate.
2. General Background
Commercial nuclear reactor vessels are positioned inside a cavity of a reactor shield structure such that there is an annular space between the reactor vessel and the shield structure. The annular space has instruments positioned therein for monitoring reactivity, accommodates thermal expansion of the reactor during operations, and provides a path for air flow from the bottom of the reactor vessel. Prior to refueling the reactor, the upper portion of the annular space is flooded with borated water to provide neutron shielding while the reactor vessel head is removed. To protect instrumentation in the lower portion of the space it is necessary to install a seal plate over the space before the water is added. The inner diameter of the seal plate rests upon the reactor vessel flange and the outer diameter is bolted to the shield structure. After refueling is completed the borated water is drained from the space and the seal plate is removed and stored to allow air flow from below the reactor. During normal reactor operations the reactor vessel is subject to radial and axial thermal expansion. Seal plates currently in use for refueling operations can not be left installed around the reactor vessel and shield structure after refueling because they are unable to accommodate the thermal expansion of the reactor vessel. Attempts at developing a permanent seal plate that does not require removal after refueling have incorporated a bellows that would accommodate the thermal expansion of the reactor vessel. This has proven to be unacceptable because the bellows traps water after the space is drained. The trapped water must then be manually removed by plant personnel, resulting in increased exposure to personnel and additional equipment maintenance. Seal plates that can not be left installed around the reactor between refuelings also present the problem of requiring storage space during the interim between refuelings. From the above it can be seen that a need exists for a reactor vessel cavity seal plate that does not have to be removed between refuelings. Such a plate must accommodate thermal expansion of the reactor, provide the necessary liquid seal during refueling operations, provide access to monitoring instruments below the plate during reactor operations, and allow air flow from below the reactor.